Multiple Andreev reflection and critical current in topological superconducting nanowire junctions

TL;DR

This paper investigates transport phenomena in topological superconducting nanowire junctions, revealing unique signatures of topology through multiple Andreev reflection and critical current behavior during the topological phase transition.

Contribution

It demonstrates how MAR current and critical current measurements can serve as indicators of topological phases and Majorana states in superconducting nanowire junctions.

Findings

MAR current exhibits features related to topology such as gap inversion and Majorana states.

Critical current remains finite at the topological transition point.

Topological signatures can be detected through transport measurements.

Abstract

We study transport in a voltage biased superconductor-normal-superconductor (SNS) junction made of semiconducting nanowires with strong spin-orbit coupling, as it transitions into a topological superconducting phase for increasing Zeeman field. Despite the absence of a fractional steady-state ac Josephson current in the topological phase, the dissipative multiple Andreev reflection (MAR) current I_dc at different junction transparencies is particularly revealing. It exhibits unique features related to topology, such as the gap inversion, the formation of Majorana bound states, and fermion-parity conservation. Moreover, the critical current I_c, which remarkably does not vanish at the critical point where the system becomes gapless, provides direct evidence of the topological transition.